1. Field of the Invention
The present invention relates to an optical disk drive, or more particularly, to an optical disk drive with laser light intensity adjustment capability.
2. Description of Related Art
Optical disks are used as a core recording medium for multimedia formats. A magneto-optical disk of 3.5 inches in diameter has storage capacities of 540M bytes and 640M bytes, well above conventionally available storage capacities of 128M bytes and 230M bytes. Thus, the magneto-optical disk has become a high-density recording medium in recent years.
In the magneto-optical disk of 3.5 inches in diameter, tracks are divided into zones for zone constant angle velocity recording (ZCAV recording) according to which the number of sectors remains the same among zones. The number of zones of a conventional medium offering the storage capacity of 128M bytes is 1, and that offering the storage capacity of 230M bytes is 10. A high-density recording medium offering the storage capacity of 540M bytes or 640M bytes put to practical use in recent years has a pitch between tracks thereon becoming narrower with an increase in recording density, thus the number of zones is increasing drastically.
The recording medium offering 640M bytes has eleven zones or a relatively small number of zones. The recording medium offering 540M bytes has eighteen zones nearly double the number of zones of conventional recording media. Optimal erasure power levels and optical recording power levels of magneto-optical disks differ from medium to medium. When a medium is loaded, glow adjustment is performed for optimizing an erasure power level and recording power level.
As described in, for example, the Japanese Unexamined Patent Publication No. 9-293259, test writing is performed in inner and outer circumferential zones. The recording power levels for intermediate zones are calculated by linearly approximating them to the recording power levels for the inner and outer circumferential zones. Thus, glow adjustment is achieved.
On the conventional recording medium offering 128M bytes or 230M bytes, data is recorded by pit position modulation (PPM). The power level of glow may be changed in two stages or changed between an erasure power level and recording power level. For the recording medium offering 540M bytes or 640M bytes, recording based on pulse width modulation (PWM) is adopted to raise the recording density. For PWM-based recording, the power level of glow must be changed in four stages; that is, changed among an erasure power level, a first writable power level, a second writable power level, and a third writable power level.
The following is based on recording data on a magneto-optical disk which, in this example, offers the storage capacity of 540 bytes or 640M bytes in conformity with the ISO/IEC 15041. Recording data on this type of magneto-optical disk differs from recording data on a conventional magneto-optical disk. Specifically, for representing a value xe2x80x9c1xe2x80x9d out of two values xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d, the writing start and end pulses of a recording signal (hereinafter, xe2x80x9cedgesxe2x80x9d) are used but the recording signal itself is not. In this edge recording, the edges of the recording signal are requested to offer a good jitter characteristic.
This magneto-optical disk, as shown in FIG. 35, has a preheat power level (P1), a leading edge recording power level (P2), and a trailing edge recording power level (P3). The preheat power level P1 raises the temperature of a medium prior to recording of a signal. The leading edge recording power level P2 and trailing edge recording power level P3 independently establish the leading and trailing edges of a signal. A pulse train exhibiting three power level values is used to record data to avoid thermal interference of the leading and trailing edges. The pulse train has pulses, which exhibit the leading and trailing edge recording power levels P2 and P3, arranged in the form of a comb with the preheat power level P1 defining the base level.
As mentioned above, an optimal power level of a magneto-optical disk differs with temperature and from medium to medium. It is therefor necessary to establish a power level for each zone by test writing.
According to, for example, Japanese Unexamined Patent Publication No. 63-108539, a cartridge accommodating an optical recording medium has a magnetic information recording portion on which the conditions for optical recording are recorded. When the cartridge is loaded, the magnetic information is read to determine the conditions for recording data on, reproducing data from, and erasing data from the optical recording medium.
Moreover, according to Japanese Unexamined Patent Publication No. 2-308425, the conditions for recording compatibly with disks are stored in a recording means in advance. When a disk is loaded, information is read from a disk controller track. The information includes, for example, the conditions for manufacturing a disk including the condition that the disk must be vendor-unique. The conditions for recording, reproducing, and erasing data that are compatible with an inserted disk are selected from among the stored conditions for recording. Glow adjustment is thus carried out.
When a medium is loaded, test writing is carried out in order to optimize an erasure power level and recording power level. Glow adjustment may thus be achieved. According to, for example, Japanese Unexamined Patent Publication No. 62-285258, standard data is stored in a ROM or the like in advance. To begin with, ambient temperature is measured. A driving current associated with the ambient temperature is retrieved from the standard data in relation to the radius of each magneto-optical disk. A semiconductor laser is driven with the driving current that is a rectangular wave having a duty ratio of 50%. Test writing is performed on a magneto-optical disk. A light-receiving device and a secondary strain detection circuit are used to reproduce data recorded during the test writing. The driving current with which the semiconductor laser is driven is varied so that the duty ratio of the reproduced signal will be 50%, hence the output of the secondary strain detection circuit will be negligible. Recording and reproducing are repeated, thus establishing a power level for each zone.
The duty ratio of the reproduced signal described in the Japanese Unexamined Patent Publication No. 62-285258 varies according to the irregular sensitivity of a magneto-optical disk or a rotary deviation thereof. This means that it is impossible to establish precisely a power level according to the method involving the duty ratio of the reproduced signal.
The new generation of magneto-optical recording media is foreseen to have narrower recording tracks. Thus, the diameter of a laser light spot restricted by the wavelength of laser light and the numerical aperture (NA) of an optical system may become larger than the pitch between tracks. Nevertheless, an attempt may be made to erase data from a track with the erasure power level attained by driving a semiconductor laser with a direct current (DC) causing the semiconductor laser to glow. In this case, recording signals representing data written on adjoining tracks may be erased with heat stemming from a spot of laser light exhibiting the erasure power level. In other words, so-called cross erasure may occur. Consequently, data storage on ever-narrowing recording tracks will become increasingly difficult.
An object of the present invention is to provide an optical disk drive capable of establishing precisely at least one of a recording power level and an erasure power level.
Another object of the present invention is to provide an optical disk drive capable of establishing precisely at least a recording power level.
Still another object of the present invention is to provide an optical disk drive capable of establishing precisely an erasure power level while preventing at lease cross erasure attributable to narrow tracks on a high-density medium.
An optical disk drive is accordance with the present invention comprises a laser control means, an information reproducing means, an amplitude measuring means, and a power calculating means. The laser control means arbitrarily controls the power of laser light to be irradiated onto a test area on a recording medium. The information reproducing means reads and reproduces recording information, which has been recorded with the power level, from the recording medium. The amplitude measuring means measures the amplitude of a reproduced signal provided by the information reproducing means. The power calculating means calculates at least one of the recording power level and erasure power level according to a test power level. Specifically, the laser control means sequentially varies the power of laser light irradiated onto the test area on the recording medium. The amplitude measuring means measures the amplitude of the reproduced signal representing data acquired from the test area. The test power level is selected such that the measured amplitude falls within a predetermined range.
In the optical disk drive according to the present invention, the laser control means sequentially varies the power of laser light irradiated onto the test area on the recording medium. The amplitude measuring means measure the amplitude of the reproduced signal representing data acquired from the test area. Based on a test power level, selected such that the measured amplitude falls within a predetermined range, the power calculating means calculates at least one of the recording power level and erasure power level. Thus, at least one of the recording power level and erasure power level can be set precisely.
Other features and advantages of the present invention will be fully apparent from the description below.